The little girl wears a serious expression and a sumptuous lace-trimmed gown, which the green parrot perched at her right nearly upstages. “She’s three weeks old,” says Catherine Weiss, referring to when she and her husband, Mark, founder of London’s Weiss Gallery (+44.20.7409.0035, www.weissgallery.com), discovered the 17th-century painting. “We know she’s a princess of some sort. The dress was the clue. In a couple of weeks, we’ll know who she is.”

The 22-year-old gallery deals in European portraits from the 15th through the 18th centuries, but Catherine says that its mission is broader: “We specialize in finding and rediscovering paintings that have lost their identities.” A recent example is a profile portrait of Sir Thomas Wyatt the Younger that the Weisses attribute to Hans Holbein the Younger, who rendered famous portraits of England’s King Henry VIII. After the painting failed to sell at a July 2006 Sotheby’s sale because of concerns about its condition and its authenticity, Mark asked its owner to let him investigate. Several months of restoration work (which included cleanings that removed layers of varnish and better revealed the painting underneath), scientific testing, and consultation with Holbein experts convinced him that the painting was real. The portrait passed muster with the vetting committee of the European Fine Art Fair (TEFAF), which permitted the gallery to bring it to the March fair with a price tag of $10 million. “Mark knows it’s a Holbein due to his connoisseurship,” Catherine says. “He knows what he’s looking at. That’s what he’s good at.”

Lillian Heidenberg’s 32-year-old Manhattan gallery, Lillian Heidenberg Fine Art (212.628.6110, www.heidenbergfineart.com), deals in modern and contemporary masters such as Jean Arp and Tom Wesselman, but she went in a slightly different direction last February, when she displayed an exhibit of works by contemporary Chinese artists. “It contrasts [with what I have offered in the past], but it also fits in,” she says. “Quality art from any country fits in, and the Chinese artists I spoke to are international artists.”

The artists wrestle with ideas that are relevant to viewers throughout the world. Heidenberg displayed colorful paintings by Wang Guangyi—who explores the collision of capitalism and socialism by combining Mao-era propaganda images with the logos of Western brands such as Cartier, Chanel, and Kodak—and Zhang Dali, who covers canvases with the term “AK-47,” the name of an assault rifle that the Chinese military used against pro-democracy protestors at Tienanmen Square in 1989, and who renders portraits of migrant workers in the repeated letters and numbers. The gallery sold more than 20 works and introduced scores of visitors to Chinese contemporary art. “A lot of people who came had not heard of any of these artists and were quite enamored,” says Heidenberg. “I think it’s the beginning of a market.”

“I deal in what I like, and I don’t like Dutch old masters. I find them rather boring,” says Guy Stair Sainty, founder of London and New York’s Stair Sainty Gallery (+44.207.493.4542, 212.288.1088, www.europeanpaintings.com), explaining that he prefers French, Spanish, and Italian old masters because “often the stories [depicted] are deeply emotional stories of love, passion, and betrayal.”

Two powerful works that he exhibited in March belonged to the gallery’s other major focus, French paintings from 1800 to 1920, but both also exemplify the qualities that Stair Sainty enjoys. The Anger of Achilles, an 1825 work by Jacques-Louis David, shows the instant when Agamemnon obeys Achilles’ command to sacrifice his daughter, Iphigenia, to fulfill a promise that he made to the god Artemis. Clytemnestra, Agamemnon’s wife and Iphigenia’s mother, captures attention because of her red-eyed anguish over her child’s impending death and her inability to stop it. Lucien Lévy-Dhurmer’s 1899 canvas Eden: Passion also portrays its subject at a fateful moment: Eve, just before she tastes the forbidden fruit. Lévy-Dhurmer paints a blissful, seated maiden with Adam standing next to her, holding her hand and whispering in her ear as the snake, coiled around Eve’s ankles, watches from below. Stair Sainty made Eden: Passion the lead attraction of a separate room, though its artist is little known. “I like to find paintings that are poorly categorized, made by artists who are not well understood, and explain them to people,” Stair Sainty says. “It’s much more interesting than [just] buying and selling paintings.”